A characteristic velocity for gas-fed PPT performance scaling

Abstract

The performance scaling of gas-fed pulsed plasma thrusters (GFPPTs) is investigated theoretically and experimentally. A characteristic velocity for GFPPTs that depends on the inductance-per-unit-length and the square root of the capacitance to initial inductance ratio has been identified. An analytical model of the discharge current predicts the efficiency to be proportional to the GFPPT performance scaling number, defined here as the ratio of the exhaust velocity to the GFPPT characteristic velocity. To test the validity of the predicted scaling relations, the performance of two rapid-pulse-rate GFPPT designs, PT5 (coaxial electrodes) and PT9 (parallel-plate electrodes), has been measured over 70 different operating conditions with argon propellant. The measurements demonstrate that the impulse bit scales linearly with the integral of the discharge current squared as expected for an electromagnetic accelerator. The measured performance scaling in both electrode geometries is shown to be in good agreement with theoretical predictions using the performance scaling number. Normalizing the exhaust velocity and the impulse-to-energy ratio by the GFPPT characteristic velocity collapses almost all the measured data onto single curves that represent the scaling relations for these GFPPTs.

Scaling laws for electromagnetic pulsed plasma thrusters

“…This implies that the capacitor voltage at the end of the discharge is zero and that current no longer flows after t f inal . Once again, we use equations (11) and (13) to model the discharge current waveform and we find that…”

“…The impulse measurements are made using an impulsive swinging-gate thrust stand where the impulse is found from the time history of the oscillating response of the thrust stand using a laser interferometer [20] or a radio-frequency proximeter [19] yielding measurement errors below 2% as described in these references. The performance of PT5 is presented in detail in [3], and the performance of PT9, with and without sidewalls, is presented in [11]. A short summary of these measurements will be provided in this section.…”

“…In [12], Pyrex sidewalls were used with PT9 to contain the propellant injected prior to the discharge. In [11] it was shown that the performance of PT9 improved without sidewalls, especially at the lowest mass bit values where the exhaust velocity is the highest. Although the sidewalls help to contain the propellant before the discharge and focus the exhaust stream, they also can significantly retard any moving ions that collide with them and recombine on the surface.…”

“…More recently a series of GFPPTs were developed and studied with the goal of revealing some of the fundamental performance scaling laws of electromagnetic pulsed plasma thrusters (EM-PPTs) [3,[11][12][13][14]. Using modern solid-state pulse forming technology to group a series of low-energy (<10 J) pulses together in bursts, we were able to maintain the propellant mass utilization efficiency near 100% while eliminating the need for an ultra-fast valve with exceptional lifetime characteristics.…”

Experimental characterization of a coaxial plasma accelerator for a colliding plasma experiment

“…9 Further applications for single plasma accelerators include x-ray lithography, laboratory modeling of astrophysical jets, and thruster for the propulsion in space and plasma refueling for fusion reactors. [10][11][12][13] Colliding plasmas were suggested for application in high energy density physics, 14 experimental applications in astrophysics, specifically galactic outflows, 3,13 and also as driver for magnetoinertial fusion. [15][16][17] Similar to a Marshall-type set-up, no magnetic field was applied in the coaxial plasma accelerator presented here.…”